527 
Cranoceras. 
This genus was described in Genera of Fossil Cephalopod, 
p- 281, for a series of cyrtoceran forms having in the Silurian rep- 
resentatives like Cranoceras (Cyri.) hospitale, sp. Barrande, PI. 
as TET peaeruM bl. tan and Purnws, Pls“ 489"! and “484.” 
The whorls are subtrigonal with the dorsum, much wider than the 
venter, which is apt to be elevated and subangulated. ‘The young, 
until they are quite large, are compressed elliptical in section, with 
the ventro-dorsal diameter longer than the transverse, then expand- 
ing more rapidly they become more depressed and take on the 
subtrigonal outline, the dorsum broader than the venter, which in 
some species changes subsequently into the nephritic with a slight 
impressed zone, Fig. 43, Pl. viii. 
The sutures have ventral saddles, slight lateral lobes and slight 
broad dorsal lobes, but in some species may be approximately 
straight and in the young stages are of this character in most forms. 
Considering the size of the shells the septa are remarkably close 
and numerous, and only slightly concave. 
The siphuncle is propioventran and apt to be filled with radia- 
ting deposits. The Silurian forms do not have the nephritic out- 
line and also have no impressed zone at any stage, judging from the 
large shell of Cranoceras turnus, which, although it has a nautilian- 
like form in the large fragment described by Barrande, probably 
did not coil very closely. 
The Devonian forms are, however, more interesting in connec- 
tion with the history of the impressed zone. These can be included 
under the names of Cranoceras (Cyrt.) depressum and Cranoceras 
(Cyrt.) lineatum. 
In the Museum of Comparative Zodlogy, in the Schulze collec- 
tion from Pelm near Gerolstein, in the Eifel, there is a specimen of 
Cranoceras lineatum 159 mm. in length along the median lateral line, 
transverse diameter of smaller end 45 mm., abdominodorsal 41 mm., 
and diameters of larger end 109 mm. and 85 mm. This is evi- 
dently a quick-growing and very large specimen, but showing no 
signs of having been coiled. It has, however, near the larger end 
on the incurved dorsal side a very faint impressed zone given in 
the outline, Fig. 43, Pl. viii, traced from the specimen. Some 
specimens do not exhibit this depression, but most of this species 
do have similar depressions and some of these are so nearly straight 
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